Heavy metal surveys in Nordic lakes harmonised data for regional assessment of critical limits

Abstract

In the autumn of 1995, national lake surveys were conducted in the Nordic countries. The surveys were co-ordinated with respect to lake selection strategy, analytical methods, sampling techniques and sampling period. The 11 heavy metals investigated in nearly 3000 lakes show in general low values and distinct geograhical patterns. Direct and indirect influence of long-range transported air pollution is the major important factor for distribution of Pb, Cd, Zn and also to a certain degree Co. TOC-levels in lakes are important for Fe and Mn but also to a certain degree As, Cr and V. Bedrock geology is the major controlling factor for Cu and Ni, with exception of areas around the smelters at Kola, where the Cu and Ni concentrations in lakes are very high. Bedrock and overburden geology is also an important factor for controlling the concentration levels of As, Co, Cr and V. The results indicate that heavy metal pollution in lakes is a minor ecological problem on a regional sclae in the Nordic contries. Certain areas in particular in southern Norway and Sweden however, are affected by influence of long-range transport leading to increase in Pb, Cd and Zn in lakes above limits set by environmental authorities. Since aquatic biota in these areas already is under stress due to effects of acid rain, this may be an important environmental problem. Hg is not included in the Nordic Lake Survey, but from other work indicates that Hg is a significant environmental problem in many lakes, in southern Finland and Sweden.